The name of Spasticity is not correct because this is a genetic myastenia. The neuromuscular junction of the proximal muscles of the forelimbs are preferentially affected.
The disease was first described in 1974. In this time, breeders didn't know the origin. But as they saw recurred cases in several countries (Australia, New-Zealand, United-States, Great Britain
and Netherlands), they supposed it had a genetic origin. Indeed, when the breed was created in the 60's, inbreeding was necessarily made in order to determine and to fix the breed standard.
Because of this important inbreeding, the CMS of Devon Rex appeared.
Since this discover, pedigree of affected kittens were studied and breeders concluded to a recessive autosomal (as well males than females), monogenic (spt gene) hereditary transmission, because affected kittens were born from normal parents (healthy carriers: SPT/spt).
The signs commonly develop on kittens of mean age of 4 to 7 weeks, but may occure until 12 or 14 weeks.
The kitten is active and mentally normal, but he displays abnormal bearing:
- A jerky, stiff and hypermetric gait of the forelimbs (high-stepping: like a "military walk"). The kitten runs with rabbit's jumps because of a lack of limbs' suppleness.
- The shoulders blades are held high (scapula protrusion).
- The neck arches downwards with the head held low (ventroflexion). The chin sometimes touches the chest. The flexion is more marked when the kitten walks, urinates or defecates.
- He frequently stops playing for resting.
- At rest, the kitten lies flat with his head held to one side, or he sits on his back croup, or he is leaning against an upright object so as to stretch out the chest.
- Feeding is difficult because the arched neck interferes with the normal feeding action of extending the neck. Drinking is particularly messy because the nose often dips below the surface of the liquid. As a result, aspiration pneumonia is the main cause of death of affected kittens.
Severity of symptoms varies from one cat to another and from one day to another on the same cat. Periods of few days of apparent normality alternate with a general deterioration (important musculoskeletal and respiratory difficulties, intense fatigue). Life expectancy is time-varying: from few months to several years if attentive cares are made.
The affected muscular fibers are heterogeneous and degenerate. The more the animal grows old, the more the disorder becomes marked. There is no lesion of the nerves. The pathology is exclusively a muscular dystrophy secondary to a neuromuscular junction dysfunction.
No possible recovery, the disease lead to death at short, medium or long-term.